Mitosis

1. The Great DivideThe Great Divide
05/04

2. To Be Answered…To Be Answered…
THINK:
 How many cells are you composed of?
 When an organism grows bigger do you
get more cells or just bigger cells or both?
 When do your cells divide the fastest?
Slowest?
 Do cells ever stop dividing?
 Are all cells capable of division and
replacement?

3. Why Would a Cell Divide?Why Would a Cell Divide?
 As cells absorb nutrients and get larger, the
volume of the cell increases faster than the
surface area
 This means that a cell can no longer absorb
nutrients and get rid of wastes fast enough to
support its demands (volume)
 So what’s a cell to do?
Solution: divide in 2!
Surface area
for exchange
not great
enough to
support cell’s
needs

4. When Would a Cell Divide?When Would a Cell Divide?
 Growth
 Repair or Replacement
 Cancer
Different cells divide at different rates:
 Most mammalian cells = 12-24 hours
 Some bacterial cells = 20-30 minutes

5. Getting Older…Getting Older…
 All cells are only allowed to complete a
certain number of divisions
 Then they die (programmed cell death)
How does cell division change over a lifetime?
 Childhood = cell division > cell death
 Adulthood = cell division = cell death
 The Later Years = cell division < cell death

6. Getting Older…Getting Older…
 All cells are only allowed to complete a
certain number of divisions
 Then they die (programmed cell death)
How does cell division change over a lifetime?
 Childhood = cell division > cell death
 Adulthood = cell division = cell death
 The Later Years = cell division < cell death